[supra400hptt]

I'm the only one that I've seen with this problem, but when I ran my pumps off of the battery my fuel pressure would drop after starting the car. It would go down around 8 psi after a few minutes of running. I ended up hooking the walbros back up to the stock fuel pressure ecu and with regulated voltage my fuel pressure is stable now. Try it if you don't find another solution.

 

[supra400hptt]

Dual walbros and -8 here also. My pressure would be in the low 30s at start up, a few minutes latter start to drop a psi or two at a time until it ended up in the low to mid 20s. Drove me nuts. I changed pumps, regulator, put in a fuel cooler and finally rewired the pumps to the stock fuel ecu. Problem solved.

There have been several discussions on running two pumps on the stock fuel ecu. Don't do it with MKIV pumps. Ok in my experience with two walbros. Search for those threads if you want to read more.